The invention relates to a folding roller comprising on its outer shell surface rubber-elastic inserts on which roll the transport belts which at least partially wrap the folding roller. Furthermore, the invention relates to a device for forming folds, which comprises a folding roller according to the invention.
For forming folds of sheets or webs printed for example in offset, intaglio or inkjet printing machines which are separated into sheets prior to the folding operation, a so-called knife folding or chopper folding device is known from the prior art. Such a device generally consists of a folding table with a recess on which the sheet to be folded comes to lie. For forming the fold, the sheet is pressed by a folding knife through the recess of the folding table into the inlet nip of two folding rollers rotating in opposite directions. With their outer shell surfaces, the folding rollers grip the sheets, conveying these into a belt line subject to forming a fold which runs parallel to the axis of rotation of the folding rollers. This belt line usually consists of multiple transport belts arranged at a certain distance next to one another, which at least partially wrap the folding rollers. The basic function principle of such a folding device is described for example in DE574360 or in DE2837392 C3.
The folding rollers that are employed with such folding devices are likewise known from the prior art. Accordingly, DE3836342 A1 discloses a so-called clocked folding roller which does not comprise a continuous cylindrical outer shell surface. DE19956248 A1 discloses folding rollers with partial recesses in the outer shell surface of the folding roller, DE19702252 A1 describes a folding roller with a folding bar extending axially parallel alongside the folding roller. DE10304534 A1 discloses a folding roller which has a friction layer on certain parts of the shell surface.
All the folding rollers known according to the prior art however comprise transport belts circulating on these, which directly roll on the folding roller body. To ensure a unique position, these transport belts generally run in grooves extending in the circumferential direction. The transport belts employed for this purpose generally have a friction coefficient that is higher compared with the shell surface of the folding roller since the transport belts have to ensure the secure and clocked transport of the folded sheets even after the forming of the fold.
For this reason, the grooves in the folding rollers are generally dimensioned in such a manner that the transport belt slightly protrudes over the outer shell surface of the folding roller. In principle it is also possible that the at least one transport belt lies on the outer shell surface of the folding roller body and the folding roller body thus does not have a circumferential groove or grooves, which is dependent on the substrate and the folding quality to be expected. If applicable, more transport belts are required with this embodiment over the axial extension of the folding roller to ensure a more homogeneous shell surface.
In particular with thin folding products or folding products from a substrate having less grip the correct adjustment of the folding roller nip relative to the product thickness is extremely important. Too large a folding roller nip can result in that either the fold is not formed neatly or that the sheet pressed into the folding roller nip by the folding knife is not gripped by the folding rollers and thus not folded away, which leads to so-called stoppers. Too narrow a folding roller nip generally leads to squashed folds or other damage to the folded sheets and can additionally lead to huge wear of folding rollers, transport belts and/or of the folding knife.
Since through the folding operation the transport belts in particular are subject to a certain wear even with correct adjustment of the folding roller nip, the protrusion of the belts relative to the folding roller shell surface changes, which on the one hand requires readjustment of the folding roller nip and on the other hand renders the adjustment of the folding roller nip even more sensitive in particular with critical productions.
With respect to the wear but also to the transport behavior of the transport belts an aggravating fact is that the system folding roller—transport belt according to the known prior art has hardly any elasticity since the transport belts which generally are only approximately 1 to 2 mm thick and because of this the transport belts which are very stiff in this alignment run on the hard, generally metallic folding roller bodies.
The invention is therefore based on the object of creating a solution with which on the one hand the wear of the transport belts can be reduced and at the same time the adjustment of the folding rollers or of the folding roller nip can be configured less sensitive and thus less susceptible to failure.
The device according to the invention comprises a folding roller, which in at least one region in axial extension, in which at least one transport belt each wraps the folding rollers at least partially, comprises at least one rubber-elastic insert.
Such an embodiment of the folding rollers has the advantage that the at least one transport belt of the belt line does not rest on the rigid and thus inflexible folding roller body or in a circumferential groove provided on the folding roller body, so that through the rubber-elastic insert the transport belt is resilient in the radial direction of the folding roller. Because of this, a transport belt can yield parallel to the axis of rotation of the folding rollers in the radial direction when the folding knife dips into the folding roller nip and while the sheet to be folded is pressed into the folding roller nip for forming a fold which takes place because of this. On the one hand, this has the advantage that the wear of the respective transport belt compared with the prior art, with which the transport belt lies on the hard, mostly metallic and thus inflexible folding roller body or in a circumferential groove provided on the folding roller body, is significantly reduced. On the other hand, through the resilience the sensitivity of the adjustment of the folding roller nip is clearly reduced, i.e., in particular when folding thin folding products or folding products of a substrate with little grip or corresponding coating, the risk of stoppers in the case of a folding roller nip that is too small or too large or folding problems such as doubling or damage to the substrate surface with too small a folding roller nip can be noticeably reduced.
Here, there is no difference with regard to the just mentioned advantages whether the rubber-elastic insert has a width which at least corresponds to the width of the transport belt so that the transport belt over its entire width lies on the rubber-elastic insert, or if the rubber-elastic insert has a width which is smaller than the width of a transport belt so that the transport belt only partially lies on the rubber-elastic insert. For it is substantial that in at least one region over the transport belt width, in which the transport belt lies on the rubber-elastic support, a larger protrusion in the radial extension of the folding roller is present than in the regions over the width of the transport belt, in which the transport belt if appropriate does not rest on the rubber-elastic support.
In a form of the invention, the rubber-elastic insert consists of a compressible material. The advantage in this case is that when dimensioning the groove for the insert no consideration has to be given to the change in shape and the insert thus does not change for example the position relative to the folding roller body. A particular advantage of this form is the possibility of not producing the insert from one or multiple closed rings of rubber-elastic material, but to embody these as a strip with finite extension, preferentially this extension corresponds to the circumference of the respective groove. This form of the invention is explained in more detail later on.
In a further advantageous form of the invention, the rubber-elastic insert consists of incompressible material. Such a configuration offers for example the advantage that as an insert commercially available rings of rubber-like material such as for example NBR-70 or polyurethane, which are available in a large assortment and at favorable costs, which renders the procurement as well as the availability advantageous for the producer and also for the end user, can be used. Accordingly, rubber rings with a diameter of the cross-section of 2 to 10 mm can be employed for example.
Accordingly, in a further advantageous configuration of the invention, at least one rubber-elastic ring can be employed as rubber-elastic insert in each case.
This form has the advantage that the insert has no joint or no seam so that in all places in the circumferential direction of the folding roller the insert has the same characteristic. This is required in particular when non-clocked folding rollers, i.e., folding rollers on which the folding operation in the form of the dipping of the folding knife and thus the folding away of the sheets to be folded seen in the circumferential direction of the folding roller always takes place in different positions, are used. However, even with clocked folding rollers, i.e., with folding rollers where the folding operation in the form of the dipping of the folding knife and thus the folding-away of the sheets to be folded always takes place as seen in the circumferential direction of the folding roller in the same position, this embodiment of the insert is advantageous since during the assembly no absolute position of the insert relative to the folding roller body has to be observed.
For the sake of completeness it is additionally mentioned here that these rubber-elastic rings can have any cross-section, such as for example a circular, polygonal or otherwise shaped cross-section. Because of the different behavior if applicable, only the hardnesses of the materials have to be adapted to the respective cross-section in this case.
A substantial advantage of the closed rings as the insert is that these have the same characteristics in the circumferential direction of the folding roller. However, it is disadvantageous with this embodiment that the folding roller has to be removed from the folding roller mounting in order to be able to mount new inserts on the roller.
The effort required for this can be reduced in a further advantageous configuration of the invention when on the folding roller in at least a limited region of axial extension, which is not covered by transport belts, endless, at least one annular insert for stocking is accommodated. Accordingly, in the case of damage or fatigue of the inserts the worn annular and thus closed inserts can be cut open and removed from the folding roller, whereas new annular inserts from the region forming the stock are pushed into the respective groove for the insert without having to disassemble the folding roller for this purpose.
In order to entirely avoid this disassembly of a folding roller a further advantageous form of the invention is that as the insert a strip-like body with finite extension in the longitudinal direction is employed, which is preferentially clamped in the groove for the insert in the form that the insert is fixed on the folding rolling without additional fastening elements. This is effected for example in that the groove for the insert has a cross-section which in the radial direction of the folding roller has a tapering cross-section, for example a trapezium-shaped cross-section.
Such an embodiment has the advantage that for replacing the rubber-elastic insert the folding roller does not have to be disassembled, because of the existing joint of the insert such an embodiment is preferentially employed with clocked folding rollers, i.e., with folding rollers where the dipping of the folding knives in the circumferential direction of the folding roller always occurs in the same place.
A further preferential configuration of the invention is that the rubber-elastic inserts are provided in first regions in axial extension in which in a first operating state the transport belts at least partially wrap the folding roller and at the same time in second regions in axial extension in-turn at least one rubber-elastic insert is provided, so that in the case of a worn insert of the at least one first region, the transport belts in a second operating state are relocated into the places of the second regions. This configuration is possible both with inserts of endless rings and also with inserts of strips of finite extension and reduces the maintenance efforts and thus the down times.
Preferred further developments of the invention are obtained from the following description. Various exemplary embodiments of the invention are explained in more detail with the help of the drawings without being restricted thereto.